The present invention relates generally to oil well pumping units, and more particularly to an emergency system for shutting down operation of the pumping unit after a sudden loss of pumping load.
Air-balanced pumping units have been used for pumping oil from wells for many years. Such pumping units include a frame, a walking beam reciprocably mounted on the frame, a barrel pump located underground in proximity to the oil bearing formation, and a sucker rod assembly operably connecting the walking beam with the barrel pump. A pump motor, which can be electric, diesel, steam-driven or the like, reciprocates the walking beam to drive the barrel pump. An air cylinder is connected to the walking beam near its output end and is pneumatically connected to an air receiver so that energy is stored in the cylinder in the form of compressed air as the walking beam travels downward. Acting as an air spring, the cylinder returns energy to the walking beam on its upward stroke. Such air-balanced pumping units enjoy widespread use in the oil fields and have proven to be both reliable and economic in operation.
Although generally reliable, the sucker rod assemblies of such units occasionally fail due to fatigue and over stressing resulting from substantially continuous operation, sometimes over a period of years. If such failure occurs near the upper end of the sucker rod string, or at the polish rod which connects the sucker rod to the walking beam, the result is an immediate cessation of load on the pumping unit. When such loss of load occurs, the energy stored in the air cylinder and air receiver can exert a large unbalanced upward force, often exceeding 25,000 lbs, on the walking beam often can result in catastrophic failure of the unit and potential injury to nearby persons and property.
It is therefore desirable to provide a shutdown system for air-balanced pumping units which can sense a loss of load on the pump, release stored energy in the air cylinder and air receiver system, and halt pump operation with minimum stress placed on the unit.